The present invention relates to a method and a device for heat-sealing windows into folding carton blanks in order to produce liquid-proof folding cartons having film windows, film pieces that have been cut to measure being placed onto the window openings of the folding carton blanks and the edges of the film pieces being heat-sealed to the folding carton blanks in a liquid-proof manner using heated pressure segments or heat-sealing dies.
The production of folding cartons having film windows, in which film pieces are placed onto the window openings of the folding carton blanks and are fastened there, is known in various methods. For example, in De-A-31 29 496 a method is described for the continuous production of folding cartons having film windows in which a piece of film made of flexible plastic material is glued over the window opening area. Here, the film is drawn from a supply roll, cut into pieces, and glued over the pre-stamped window opening area with as precise a fit as possible.
In EP-A-1 201 417, a method is described for multi-web production of folding carton blanks having glued-on film pieces, in which block cylinders are used to apply adhesive to the window opening area of the folding carton blanks at a gluing station, and film pieces are placed onto the adhesive-coated areas using a suction cylinder. A suction belt is used to transport the folding carton blanks. If a folding carton blank is missing, the suction belt is contaminated with glue and the following folding carton blank is undesirably contaminated with glue. It is therefore necessary either to raise the entire block cylinder or to lower the suction belt. In order to avoid contamination of the following folding carton blanks given a relatively high production rate with multi-web transport, in the area of the block cylinders the suction belts are supported in such a way that only defined sub-areas of the relevant suction belt need be removed from the area of contact with the block cylinder.
In order to produce liquid-proof folding cartons having windows with a tight heat-sealing of the film window to the liquid-proof surface of the folding carton, a method is known that uses heated stamps to heat-seal the film window to the folding carton. Here, the film material is first drawn mechanically from a roller, cut to length, and placed onto the window opening of the folding carton blanks, which are laid flat. The folding carton blank is moved on a transport belt above which a heated stamp is situated that is lowered onto the film window with pressure, and is transported during the heat-sealing process with the same speed as the transport belt. After the heat-sealing is completed, the stamp moves upward and is moved back to its initial position, opposite the direction of transport of the transport belt. In order to increase efficiency, it is possible to simultaneously operate a plurality of stamps in a repetitive method; here efficiency is limited by the fact that, due to the nature of the process, the time during which the stamp is moved back to its initial position cannot be used for heat-sealing.